This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Application No. 9914701.9 filed in Great Britian on Jun. 23, 1999; the entire content of which is hereby incorporated by reference.
The present invention relates to signalling in a telecommunications network and in particular though not necessarily to ensuring the interworkability of future generation signalling networks with existing signalling networks.
Telecommunications networks currently rely to a large extent upon the Signalling System no. 7 (SS7) as the mechanism for controlling call connections and for handling the transfer of signalling information between signalling points of the networks. Typically, one or more Application and User Parts at a given signalling point will make use of SS7 to communicate with peer application and user parts at some other signalling point. Examples of User Parts are ISUP (ISDN User Part) and TUP (Telephony User Part) whilst examples of Application Parts are INAP (Intelligent Network Application Part) and MAP (Mobile Application Part). The conventional SS7 protocol stack includes Message Transfer Parts MTP1, MTP2, and MTP3 which handle the formatting of signalling messages for transport over the physical layer as well as various routing functions. The conventional physical transport network over which signalling messages are sent is a Synchronous Transfer Mode (STM) network such as E.1 (Europe) or T.1 (America). User plane data, e.g. voice information, is sent over the same STM network.
There has been considerable interest of late amongst the telecommunications community in using non-standard (i.e. non-conventional within the telecommunications industry) bearer transport mechanisms (non-STMs) in telecommunications networks for carrying user plane data. The reasons for this are related both to improvements in efficiency as well as potential cost savings. Much consideration has been given for example to the use of Asynchronous Transfer Mode (ATM) networks to transport signalling information between signalling points. The International Telecommunications Union (ITU) has recently defined a signalling protocol (specified in ITU-T Q.2630.1 and referred to hereinafter as Q.AAL2) for use in setting-up and controlling connections over ATM/AAL2 networks.
Typically, the bearer transport mechanism protocol layers lie beneath SS7, and ISUP, which deals with the setting-up and control of call connections, is closely linked to the bearer transport mechanism. ISUP therefore does not readily lend itself to use with non-STM bearer transport technologies such as AAL2. As such, several standardisation bodies including the ITU-T, ETSI, and ANSI, are currently considering the specification of a protocol for the control of calls, which is independent of the underlying bearer transport mechanism. This can be viewed as separating out from the protocol, bearer control functions which relate merely to establishing the parameters (including the start and end points) of the xe2x80x9cpipexe2x80x9d via which user plane data is transported between nodes, and which are specific to the transport mechanism. The new protocol, referred to hereinafter as Transport Independent Call Control (TICC), retains call control functions such as the services invoked for a call between given calling and called parties (e.g. call forwarding), and the overall routing of user plane data. FIG. 1a illustrates the conventional integrated Call Control and Bearer Control structure of ISUP whilst FIG. 1b illustrates the proposed new separated structure.
The current version of Q.AAL2 is designed to be used with the so-called broadband MTP layer 3, referred to as MTP3B (specified in ITU-T Q.2210). Whereas the conventional MTP3 is designed to deal with signalling messages having a maximum length of 272 octets, MTP3B is designed to deal with signalling messages having a maximum length of 4096 octets. This capability of MTP3B arises from the capabilities of a Network Nodal Interfacexe2x80x94Signalling ATM Adaptation Layer (NNI-SAALxe2x80x94see ITU-T Q.2140) which replaces the conventional MTP2. FIG. 2 compares the conventional SS7 protocol stack (shown on the left side of the FIG.) with the modified stack (shown on the right side). MTP3B and NNI-SAAL additionally facilitate a much increased signalling message throughput (millions of bits per second as opposed to 64 thousand bits per second for the conventional systemxe2x80x94hence the respective xe2x80x9cbroadbandxe2x80x9d and xe2x80x9cnarrowbandxe2x80x9d designations). In contrast to Q.AAL2, TICC is likely to specify a maximum signalling message length of 272 octets, i.e. in line with the message length restriction in conventional systems.
It is desirable to be able to carry both TICC and Q.AAL2 signalling messages over the same physical signalling network. However, this is not possible if the Q.AAL2 signalling messages can exceed 272 octets in length. The inventors of the present invention therefore propose reducing the maximum possible length of Q.AAL2 signalling messages to 272 octets.
According to a first aspect of the present invention there is provided a method of setting up and controlling a user plane connection over a bearer transport mechanism using the Q.AAL2 signalling protocol, the method comprising restricting the maximum length of the Q.AAL2 signalling messages to 272 octets.
The inventors have further recognised that NNI-SAAL signalling links will desirably be introduced initially where signalling traffic is high. For example, an NNI-SAAL signalling link could advantageously be used to couple a Signalling Transfer Point (STP) to a network node which is accessed by many other nodes via the STP, i.e. where the STP concentrates signalling traffic onto the NNI-SAAL signalling link. However, so long as conventional MTP2 based networks exist, it is necessary to ensure that new network nodes have the ability to use MTP2 or NNI-SAAL depending upon the destination of signalling messages.
According to a second aspect of the present invention there is provided a method of signalling in a telecommunications network, the method comprising:
generating signalling messages at an Application Part or a User Part of an originating signalling point, the messages having a maximum length of 272 octets;
transferring the generated signalling messages to a Message Transfer Part layer 3 (MTP3) of the originating signalling point;
on the basis of the destination signalling point of the received signalling message, determining whether or not the message is to be transmitted over an NNI-SAAL signalling link; and
if the message is to be transmitted over an NNI-SAAL signalling link, transferring the message to an NNI-SAAL part of the originating signalling point, and if the message is not to be transmitted over an NNI-SAAL signalling link, transferring the message to an MTP2 part of the originating signalling point.
Preferably, said Application Part or User Part is a Transport Independent Call Control User Part or a Q.AAL2 User Part.
In certain embodiments of the present invention, an Application Part or User Part may require signalling messages having a maximum length greater than 272 octets. It is possible to accommodate such a requirement by segmenting larger messages in the Application or User Part, and carrying out a reassembly process at the peer Part of the destination signalling point.